Monopulse radar system

ABSTRACT

To realize a monopulse radar system wherein the velocity of a mobile body, distance between an obstacle and the mobile body and relative velocity can be detected and simultaneously, the direction of the obstacle can be detected, in a monopulse radar system wherein an azimuth is detected depending upon amplitude difference or phase difference between signals respectively received by plural receiving antennas, an array antenna composed of plural antenna elements is used for each transmitting antenna and each receiving antenna, at least one of the transmitting antenna and the receiving antenna is provided with an antenna switch for switching an antenna beam shape to a short angle/long distance or a wide angle/short distance and a switch control device that controls the switching of the antenna switch is provided.

[0001] This application is a continuation in part of U.S. applicationSer. No. 10/083,339 filed on Feb. 27, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a monopulse radar system,further detailedly relates to a monopulse radar system that radiates aradio wave, receives a reflected radio wave from a body where the radiowave is detected with plural receiving antennas and detects thedirection of the detected body depending upon difference in amplitude ora phase between signals received by the plural receiving antennas andparticularly relates to a monopulse radar system suitable for a radarused for a car and mounted on a mobile body such as a vehicle.

[0004] 2. Description of the Related Art

[0005] Heretofore, a radar system used for a car and mounted on a mobilebody such as a vehicle for detecting the velocity and the position of adetected body such as the mobile body and an obstacle is known. For aradar system used for a car, a radar system used for a car in whichantenna beam width is switched from wide one to narrow one and viceversa corresponding to a detected body and the velocity and the positionof the detected body are precisely detected and a radar system used fora car in which the direction of the detected body can be detected aredeveloped.

[0006] For a document related to the former, for example, Japanesepublished unexamined patent application No. Hei 2-287181, “RADAR SYSTEMUSED FOR CAR” and Japanese published unexamined patent application No.2000-258524 can be given.

[0007] For the latter primary radar system for detecting the directionof a detected body, a mechanical scanning system of mechanically turningan antenna by a motor, a beam switching system of switching pluralantennas different in the orientation of a beam (for example, disclosedin Japanese published unexamined patent application No. Hei 8-334557)and a monopulse system (for example, described on pages 8 to 19 of“Monopulse Principles and Techniques” published by ArtechHouse andwritten by Samuel M. Sherman) can be given.

[0008] According to the monopulse system, as shown in FIG. 10, reflectedwaves 29 from an obstacle 28 are received by two receiving antennas 30and a sum signal p and a difference signal q are generated in a hybridcircuit 8. Relation between the relative electric power of the generatedsum signal p and the generated difference signal q and an azimuth is asshown in FIG. 11 and relation between the ratio t of the sum signal pand the difference signal q and an azimuth is as shown in FIG. 12. Asshown in FIG. 12, as the ratio t of the sum signal p and the differencesignal q is a monotone decreasing function in relation to an azimuth,the azimuth of a detected body can be uniquely determined based upon theratio t of the sum signal and the difference signal. High-resolutionangle detection can be also performed in a wide range by increasing thenumber of receiving antennas.

[0009] Recently, it is demanded for a radar system used for a car thatthe direction of a detected body is precisely detected at the same timeas the velocity and the position of the detected body are preciselydetected. Further, as the radar system is used for a car, it is demandedthat the radar system has simple configuration, is compact and themanufacturing cost is low. The above-mentioned conventional typemonopulse system is excellent in azimuth resolution, compared withanother system and relative miniaturization is possible. However,antenna beam width is required to be widened to enlarge a detectabledirectional range, a detectable distance range is narrowed and azimuthresolution is also deteriorated. To enlarge a detectable azimuth withoutdeteriorating detectable distance and azimuth resolution, an antennathat generates a wide angle beam and an antenna that generates a narrowangle beam are required to be provided and to be switched, and there isa problem that the system is large-sized and the cost is increased.

SUMMARY OF THE INVENTION

[0010] Therefore, the invention is made to solve the problem and it isthe object to provide a low-cost, compact and light monopulse radarsystem wherein the monopulse system is improved, a detectable range ofthe position (distance between an antenna and a detected body) of thedetected body and relative velocity can be switched to a sharpangle/long distance or a wide angle/short distance and simultaneouslythe precise azimuth of an obstacle can be detected in the range.

[0011] To achieve the object, in the monopulse radar system according tothe invention, at least one of a transmitting antenna and a receivingantenna is formed by an array antenna composed of plural antennaelements, the plural antenna elements are divided into plural groups, anantenna switch to switch the plural groups is provided and a switchcontrol device to control the opening and closing of the antenna switchis provided to switch an antenna beam of at least the transmitting orreceiving antenna to a sharp angle/long distance or a wide angle/shortdistance.

[0012] In the invention, a detectable range of distance up to a mobileobstacle and relative velocity can be switched to a sharp angle/longdistance or a wide angle/short distance by switching the antenna switchof the array antenna, simultaneously the accurate azimuth of theobstacle can be detected in the detectable range and in case antennabeams cover a sharp angle and long distance, higher-accuracy azimuthdetection is enabled. As a detection range is switched by connection anddisconnection in units of an antenna element, multiple independent arrayantennas the orientation of which is determined are not required and thesimple antenna switch is provided to the array antenna, the low-cost,compact and light system can be realized.

[0013] Beam switching technique in which the velocity of a detected bodysuch as a mobile body and an obstacle and distance up to it are detectedin a state of suitable beam width by switching beam width according todistance up to the detected body (disclosed in for example, Japanesepublished unexamined patent application No. Hei 2-287181, “RADAR SYSTEMUSED FOR CAR”) is known, however, according to the beam switchingtechnique, the azimuth of a detected body cannot be detected. In theinvention, it is first found and realized by combining beam switchingtechnique and a monopulse radar system that in case antenna beams covera sharp angle and long distance, higher-accuracy azimuth detection whichis not acquired in each of the beam switching technique and themonopulse radar system is enabled, utilizing the advantages of amonopulse radar.

[0014] As a monopulse radar system according to the invention isprovided with the antenna switch for switching beams from thetransmitting array antenna and the receiving array antenna respectivelycomposed of plural antenna elements to a sharp angle/long distance or awide angle/short distance, a detectable range of distance up to a mobileobstacle and relative velocity can be switched to a sharp angle/longdistance or a wide angle/short distance, as a monopulse system is used,the accurate azimuth of the obstacle can be detected in the range, incase antenna beams cover a sharp angle and long distance,higher-accuracy azimuth detection is enabled, the detectable range isswitched by connection and disconnection in units of an antenna elementand as plural array antennas are not required, the low-cost, compact andlight monopulse radar system can be realized.

[0015] This and other advantages of the present invention will becomeapparent to those skilled in the art on reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram showing a first embodiment of amonopulse radar system used for a car according to the invention;

[0017]FIG. 2 shows the characteristics of a sum signal and a differencesignal of a monopulse system for explaining the effect of the invention;

[0018]FIG. 3 is a block diagram showing a second embodiment of themonopulse radar system used for a car according to the invention;

[0019]FIG. 4 is a block diagram showing a third embodiment of themonopulse radar system used for a car according to the invention;

[0020]FIG. 5 is a block diagram showing a fourth embodiment of themonopulse radar system used for a car according to the invention;

[0021]FIG. 6 is a block diagram showing a fifth embodiment of themonopulse radar system used for a car according to the invention;

[0022]FIG. 7 is a block diagram showing a sixth embodiment of themonopulse radar system used for a car according to the invention;

[0023]FIG. 8 is a block diagram showing a seventh embodiment of themonopulse radar system used for a car according to the invention;

[0024]FIG. 9 is a block diagram showing an eighth embodiment of themonopulse radar system used for a car according to the invention;

[0025]FIG. 10 is an explanatory drawing for explaining the monopulsesystem;

[0026]FIG. 11 shows the characteristics of the sum signal and thedifference signal of the monopulse system; and

[0027]FIG. 12 shows the characteristic of the ratio of the sum signaland the difference signal of the monopulse system.

[0028]FIG. 13 is a plane view showing one embodiment of a transmittingarray antenna used in a monopulse radar system according to thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]FIG. 1 is a block diagram showing the configuration of a firstembodiment of a monopulse radar system used for a car according to theinvention. In this embodiment, a signal is transmitted from atransmitting and receiving device 9 via a transmitting array antenna 1composed of plural antenna elements 1 a to 1 j, the signal reflected onan obstacle is received by a first receiving array antenna 2 composed ofplural antenna elements 2 a to 2 e and a second receiving array antenna3 composed of plural antenna elements 3 a to 3 e, and a sum signal and adifference signal respectively generated in a hybrid circuit 8 are sentto the transmitting and receiving device 9.

[0030] The configuration of the transmitting and receiving device 9 isidentical to that of a heretofore known monopulse radar system. Amillimeter-wave signal from an oscillator 11 is applied to thetransmitting array antenna 1 via a power amplifier 12. The sum signal pand the difference signal q respectively generated in the hybrid circuit8 are respectively applied to mixers 13 a and 13 b, are mixed with asignal output from the oscillator 11, are respectively converted to anintermediate-frequency signal and are respectively input to a signalprocessing circuit 14. The signal processing circuit 14 detects theazimuth of a detected body using signals acquired by converting thefrequency of the sum signal p and the difference signal q and detectsthe velocity and the position of the detected body using the sum signalp. The result of the detection is converted to a signal suitable for anoutput device 15 such as a display if necessary and is output to theoutput device 15.

[0031] In this radar system, as a beam shape from/to the transmittingarray antenna 1 and the receiving array antennas 2 and 3 is switched toa sharp angle/long distance or a wide angle/short distance, thetransmitting array antenna 1 has plural groups of antenna elements 1 ato 1 c, 1 d to 1 g and 1 h to 1 j and antenna switches 4 and 5 forconnecting or disconnecting each antenna element group, and thereceiving array antennas 2 and 3 respectively have plural groups ofantenna elements 2 a to 2 c and 2 d to 2 e and plural groups of antennaelements 3 a to 3 c and 3 d to 3 e and antenna switches 6 and 7 forconnecting and disconnecting each antenna element group. Further, aswitch control device 10 that controls the turning on or off of theantenna switches 4 to 7 is provided. For example, when the antennaswitches 4 to 7 are turned on by the switch control device 10 and theplural antenna elements 1 a to 1 j, 2 a to 2 e and 3 a to 3 e areconnected, a beam shape from the transmitting array antenna 1 is turneda sharp angle/long distance as shown by full lines st and sr in FIG. 1and as antenna aperture length is reduced when the antenna switches 4 to7 are turned off, that is, the antenna switches 4 to 7 are disconnectedfrom the groups of antenna elements respectively composed of pluralantenna elements 1 a to 1 c, 1 h to 1 j, 2 a to 2 c and 3 a to 3 c, abeam shape from/to the transmitting array antenna 1 and the receivingarray antennas 2 and 3 is turned a wide angle/short distance as shown bydotted lines wt and wr in FIG. 1. As described above, the detectablerange of distance up to a mobile obstacle and relative velocity can beswitched to a sharp angle/long distance or a wide angle/short distanceby switching the antenna switches 4 to 7.

[0032] As in this embodiment, a monopulse system is used, the accurateazimuth of an obstacle can be detected in the range and in case antennabeams cover a sharp angle and long distance, higher-accuracy azimuthdetection is enabled. That is, as shown in FIG. 2, when an antenna beamshape is switched, the relation tw of a monotone decreasing function twwhen an antenna beam shape is a wide angle/short distance is kept forrelation between the ratio t of a sum signal p and a difference signal qand an azimuth and as the inclination of the ratio of the sum signal pand the difference signal q is abrupt as a curve ts in case an antennabeam shape is a sharp angle/long distance, an azimuth can be preciselydetected.

[0033] As a detection range is switched by connection and disconnectionin units of the antenna element and plural array antennas are notrequired, the low cost, miniaturization and lightening can be realized.The antenna switches 4 to 7 are not particularly required to beinterlocked and various detection ranges can be acquired by individuallyswitching.

[0034] Various detection ranges can be acquired by increasing the numberof the antenna elements and the antenna switches respectively shown inFIG. 1 or by varying the ratio of the transmitting array antenna 1 andthe receiving array antennas 2 and 3 and azimuth resolution can beenhanced. In this embodiment, the two receiving array antennas areprovided, however, the similar various detection ranges can be acquiredand azimuth resolution can be enhanced by increasing the number.

[0035]FIG. 3 is a block diagram showing the configuration of a secondembodiment of the radar system according to the invention. A monopulseradar system used for a car equivalent to this embodiment ischaracterized in that an antenna beam shape is switched by only atransmitting antenna 1, the configuration and the control of receivingantennas 2 and 3 are simplified, the system is simplified and the costis reduced.

[0036] A signal is transmitted from a transmitting and receiving device9 via the transmitting array antenna 1 composed of plural antennaelements 1 a to 1 j, the signal reflected on an obstacle is received bythe receiving array antenna 2 composed of plural antenna elements 2 a to2 e and the receiving array antenna 3 composed of plural antennaelements 3 a to 3 e, a sum signal and a difference signal respectivelygenerated in a hybrid circuit 8 are sent to the transmitting andreceiving device 9, and the velocity of a mobile body, the direction ofan obstacle, distance up to the mobile body and relative velocity aredetected. In this radar system, antenna switches 4 and 5 for connectingand disconnecting antenna element groups respectively composed of pluralantenna elements 1 a to 1 c and 1 h to 1 j for switching a beam shapefrom the transmitting array antenna 1 to a sharp angle/long distance ora wide angle/short distance and a switch control device 10 that controlsthe turning on or off of the antenna switches 4 and 5 are provided.

[0037] For example, when the antenna switches 4 and 5 are turned on bythe switch control device 10 and the plural antenna elements 1 a to 1 jare connected, a beam shape from the transmitting array antenna 1 isturned a sharp angle/long distance as shown by a full line st in FIG. 3and as antenna aperture length is reduced when the antenna switches 4and 5 are turned off, that is, antenna element groups respectivelycomposed of the plural antenna elements 1 a to 1 c and 1 h to 1 jconnected by the antenna switches 4 and 5 are disconnected, a beam shapefrom the transmitting array antenna 1 is turned a wide angle/shortdistance as shown by a dotted line wt. As described above, thedetectable range of distance up to a mobile obstacle and relativevelocity can be switched to a sharp angle/long distance or a wideangle/short distance by switching the antenna switches 4 and 5. Variousdetection ranges can be acquired by increasing the number of the antennaelements and the antenna switches respectively shown in FIG. 4 or byvarying the ratio of antenna elements in the transmitting array antenna1 and the receiving array antennas 2 and 3 and azimuth resolution can beenhanced. In this embodiment, the two receiving array antennas areprovided, however, the similar various detection ranges can be acquiredand azimuth resolution can be enhanced by increasing the number.

[0038]FIG. 4 is a block diagram showing the configuration of a thirdembodiment of the radar system according to the invention. A monopulseradar system used for a car equivalent to this embodiment ischaracterized in that an antenna beam shape is switched by only areceiving antenna, the configuration and the control of a transmittingantenna are simplified, the system is simplified and the cost isreduced.

[0039] A signal is transmitted from a transmitting and receiving device9 via a transmitting array antenna 1 composed of plural antenna elements1 a to 1 j, the signal reflected on an obstacle is received by areceiving array antenna 2 composed of plural antenna elements 2 a to 2 eand a receiving array antenna 3 composed of plural antenna elements 3 ato 3 e, a sum signal and a difference signal respectively generated in ahybrid circuit 8 are sent to the transmitting and receiving device 9,and the velocity of a mobile body, the direction of an obstacle,distance up to the mobile body and relative velocity are detected. Inthis radar system, antenna switches 6 and 7 for connecting anddisconnecting antenna element groups respectively composed of pluralantenna elements 2 a to 2 c and 3 a to 3 c for switching a beam shape tothe receiving array antennas 2 and 3 to a sharp angle/long distance or awide angle/short distance and a switch control device 10 that controlsthe turning on or off of the antenna switches 6 and 7 are provided. Theconfiguration of the transmitting and receiving device 9 is identical tothat shown in FIG. 1 and the description is omitted. For anothercomponent, the same reference number as that in FIG. 1 is allocated tothe substantially same component as that shown in FIG. 1. In the otherembodiments described afterward, it is identical.

[0040] For example, when the antenna switches 6 and 7 are turned on bythe switch control device 10 and the plural antenna elements 2 a to 2 eand 3 a to 3 e are respectively connected, a beam shape to the receivingarray antennas 2 and 3 is respectively turned a sharp angle/longdistance as shown by a full line in FIG. 4 and as antenna aperturelength is reduced when the antenna switches 6 and 7 are turned off, thatis, the antenna switches 6 and 7 respectively disconnect antenna elementgroups respectively composed of plural antenna elements 2 a to 2 c and 3a to 3 c, a beam shape to the receiving array antennas 2 and 3 isrespectively turned a wide angle/short distance as shown by a dottedline in FIG. 4. As described above, the detectable range of distance upto a mobile obstacle and relative velocity can be switched to a sharpangle/long distance or a wide angle/short distance by switching theantenna switches 6 and 7.

[0041] Various detection ranges can be acquired and azimuth resolutioncan be enhanced by increasing the number of the antenna elements and theantenna switches respectively shown in FIG. 4 or by varying the ratio ofthe transmitting array antenna 1 and the receiving array antennas 2 and3. In this embodiment, the two receiving array antennas are provided,however, the similar various detection ranges can be acquired andazimuth resolution can be enhanced by increasing the number.

[0042]FIG. 5 is a block diagram showing the configuration of a fourthembodiment of the radar system according to the invention. A monopulseradar system used for a car equivalent to this embodiment ischaracterized in that the system is simplified and the cost is reducedby sharing a transmitting antenna and a receiving antenna.

[0043] A signal is transmitted or received via the transmitting andreceiving common array antennas 11 and 12 respectively composed ofplural antenna elements 11 a to 11 e and 12 a to 12 e by a transmittingand receiving device 9, and the velocity of a mobile body, the directionof an obstacle, distance up to the mobile body and relative velocity aredetected by a sum signal and a difference signal respectively generatedin a hybrid circuit 8. In this radar system, antenna switches 6 and 7for connecting and disconnecting antenna element groups respectivelycomposed of the plural antenna elements 11 a to 11 c and 12 a to 12 cfor switching a beam shape from/to the transmitting and receiving commonarray antennas 11 and 12 to a sharp angle/long distance or a wideangle/short distance and a switch control device 10 that controls theturning on or off of the antenna switches 6 and 7 are provided.

[0044] For example, when the antenna switches 6 and 7 are turned on bythe switch control device 10 and the plural antenna elements 11 a to 11e and 12 a to 12 e are respectively connected, a beam shape from/to thetransmitting and receiving common array antennas 11 and 12 is turned asharp angle/long distance as shown by a full line in FIG. 5 and asantenna aperture length is reduced when the antenna switches 6 and 7 areturned off, that is, antenna element groups respectively composed of theplural antenna elements 11 a to 11 c and 12 a to 12 c are respectivelydisconnected, a beam shape from/to the transmitting and receiving commonarray antennas 11 and 12 is respectively turned a wide angle/shortdistance as shown by a dotted line in FIG. 5. As described above, thedetectable range of distance up to a mobile obstacle and relativevelocity can be switched to a sharp angle/long distance or a wideangle/short distance by switching the antenna switches 6 and 7. In thisembodiment, the two transmitting and receiving common array antennas areprovided, however, the similar various detection ranges can be acquiredand azimuth resolution can be enhanced by increasing the number.

[0045]FIG. 6 is a block diagram showing the configuration of a fifthembodiment of the radar system according to the invention. Thisembodiment is characterized in that a timing control device 23 isprovided to the first embodiment shown in FIG. 1 and a signal forswitching antenna switches 4 to 7 is output to a switch control device10 every fixed time. A detection range is respectively switched byswitching the antenna switches 4 to 7 every fixed time, and the errorrecognition of an obstacle and undetection can be prevented. It isdescribed above that in the fifth embodiment, the timing control device23 is provided to the first embodiment, however, it need scarcely besaid that the fifth embodiment can be also applied to the second tofourth embodiments.

[0046]FIG. 7 is a block diagram showing the configuration of a sixthembodiment of the radar system according to the invention. A radarsystem used for a car equivalent to this embodiment is characterized inthat the velocity of a mobile body itself is also detected. Thisembodiment is characterized in that a velocity judgment device 24 isprovided to the first embodiment shown in FIG. 1, the velocity of amobile body on which the radar system is mounted is judged based uponthe output of a transmitting and receiving device 9 and a switch controldevice 10 controls the switching of antenna switches 4 to 7 according tothe output of the velocity judgment device 14. Concretely, as thedetection of a remote obstacle and the prevention of an unnecessaryreflected wave from the vicinity of the mobile body are required whenthe velocity of the mobile body is fast for example, the antennaswitches 4 to 7 are respectively turned on to turn a beam shape to asharp angle/long distance, and as a remote obstacle is conversely notrequired to be detected and an obstacle in the vicinity of the mobilebody is required to be detected when the velocity of the mobile body isslow, the antenna switches 4 to 7 are respectively turned off to turn abeam shape to a wide angle/short distance. If the number of antennaelements and the switches is increased, a few beam shapes can beswitched according to the velocity of the mobile body. As describedabove, optimum obstacle detection according to the velocity of themobile body is enabled.

[0047] The case that a beam shape is switched according to the velocityof the mobile body on which the radar system is mounted is describedabove, however, needless to say, a beam shape can be also switchedaccording to relative velocity with an obstacle. Further, it isdescribed above that in the sixth embodiment, the velocity judgmentdevice 14 is provided to the first embodiment, however, the sixthembodiment can be also applied to the second to fourth embodiments.

[0048]FIG. 8 is a block diagram showing the configuration of a seventhembodiment of the radar system according to the invention. Thisembodiment is characterized in that a distance judgment device 25 isprovided to the first embodiment shown in FIG. 1, distance between amobile body and an obstacle is judged based upon the output of atransmitting and receiving device 9 and the operation of a switchcontrol device 10 is controlled based upon the output of the distancejudgment device 25. For example, in case distance between the mobilebody on which the radar system is mounted and the obstacle is long, abeam shape is turned a sharp angle/long distance to enable detecting theremote obstacle and in case distance between the mobile body and theobstacle is short, a beam shape is turned a wide angle/short distance toenable detecting only the obstacle in the vicinity of the mobile body.It is described above that in the seventh embodiment, the distancejudgment device 25 is provided to the first embodiment, however, theseventh embodiment can be also applied to the second to fourthembodiments.

[0049]FIG. 9 is a block diagram showing the configuration of an eighthembodiment of the radar system according to the invention. Thisembodiment is characterized in that a position judgment device 26 isprovided to the first embodiment shown in FIG. 1, position informationfrom a position information retrieval system 27 such as a car navigationsystem mounted on a mobile body is judged by the position judgmentdevice 26 and the operation of a switch control device 10 is controlledbased upon the output of the position judgment device 26. For examplewhile a mobile body on which a radar system and a car navigation systemare mounted runs on a highway, a beam shape is turned a sharp angle/longdistance to enable detecting a remote obstacle and while the mobile bodyruns on a general road in an urban area, a beam shape is turned a wideangle/short distance to enable detecting obstacles in a wide range inthe vicinity of the mobile body.

[0050] It is described above that in the eighth embodiment, the positionjudgment device 26 is provided to the first embodiment, however, theeighth embodiment can be also applied to the second to fourthembodiments.

[0051] The array antennas in the first to eighth embodiments are formedon a dielectric substrate. For example, a patch antenna and a tri-plateantenna are used, a simple device such as FET is mounted on plural patchgroups on the substrate as the antenna switch, a driving power sourceformed by a simple device such as FET can be simply built so that adriving signal is supplied from the rear surface via the dielectricsubstrate and miniaturization, lightening and the reduction of the costare further enabled.

[0052]FIG. 13 is a plane view showing one embodiment of a transmittingarray antenna used in a monopulse radar system according to thisinvention.

[0053] Patch trains 1 a˜1 j each having a plurality of patch (orantenna) elements and main feeder line 36, branch feeder lines 37 areformed on a dielectric substrate 31, and compose a patch array antenna1.

[0054] Each of the patch trains is connected with branch feeder lines 37arranged in parallel.

[0055] Antenna switch 4 a and 5 a respectively are disposed betweenpatch train 1 c and 1 d and between patch train 1 g and 1 h of mainfeeder line 36, which intersects perpendicular to branch feeder lines37.

[0056] When antenna switch 4 a and 5 a are turned ON, beam of sharpangle/long distance is formed, since electric power inputted from thepower supply part 32 is supplied to all of patch trains 1 a˜1 j. Andwhen antenna switches 4 a and 5 a are turned OFF, beam of a wide angeland a short distance is formed, since electric power inputted from thepower supply part 32 is supplied to only patch trains 1 d-1 g.

[0057] Antenna switch 4 a and 5 a, which are MMIC consisted of GaAs etc.is turned on or turned off by operating the bias between the groundingline 33 grounded by the via hole, and bias terminals 34 a, and 34 b.

[0058] Unnecessary radiation at the time of switch-off can be preventedby making dielectric length Ls between patch train 1 d and antennaswitch 4 a and between patch train 1 g and antenna switch 5 a as ½dielectric wavelength.

[0059] The grounding line 33 and the power supply part 32 are connectedby the short circuit line 35 having ¼ dielectric wavelength in length.Accordingly, short circuit is formed in signal line for direct currentand low frequency region and a high impedance or OFF is formed inparallel for using frequency signal, all of static electricity andundesirable waves from the antenna side fall into earth. Therefore,there is no influence on the necessary high frequency component. Byusing the grounding line as ground terminals of antenna switches 4 a, 5a there is no necessity for adding terminals on dielectric substratenewly and it is possible to reduce cost of the antenna.

[0060] In addition, the above-mentioned grounding line, a short circuittrack, etc. may be arranged on the high frequency mounting circuit planewhere an oscillator and a power amplifier are mounted.

[0061] Although all the intervals of patch trains have usually onedielectric wavelength since patch array antenna needs to excite allpatch(es) by same phase, the dielectric lengths Le for patch train 1 cand 1 d and for 1 g and 1 h are smaller than the dielectric length Lp ofother patch trains, since the patch array antenna of this embodimentconsisted of on high dielectric substrate has antenna switch is arrangedon MMIC formed on a high dielectric substrate.

[0062] There are a case that an unnecessary grating lobe may appear anda case that an antenna gain may be spoiled if the free space length of apatch train interval are uneven. Then, all the free space length of apatch train intervals can be fixed, and can rectify only a phase bybranching patch train 1 a-1 c and 1 h-1 j aslant.

[0063] Concerning to a receiving array antenna, it can carry outsimilarly by preparing hybrid circuit in the power supply part 32 oftransmitting array antenna. Moreover, the beam form can be changedeffectively by use of MEMS high frequency switch having large isolationat the time of switch-off.

[0064] Although this antenna is explained as an antenna used for thefirst embodiment, this antenna is able to be used for the 2nd to 8thembodiments. In addition, although antenna switches used in each of theembodiments are formed by use of a switch of MMIC which consisted ofsemiconductor elements in order that the antenna switches may berealized in small lightweight, and economically, it is possible tochange the beam shape effectively by using a machine switch with highisolation at the time of switch-off and low loss at the time ofswitch-on.

[0065] Although above-mentioned embodiments are explained as used forthe radar system for vehicles, it is clear that above-mentionedembodiments can be used for uses other than for vehicles.

[0066] Miniaturization, lightening and the reduction of the cost can befurther expected by using MMIC formed by a semiconductor device for theantenna switch in each embodiment. A beam shape can be efficientlyswitched by using a mechanical switch the loss of which is low when themechanical switch is turned on and which completely isolates when it isturned off for the antenna switch. In the above-mentioned eachembodiment, the radar system used for a car is described, however, it isclear that the radar system can be used for application except avehicle.

[0067] Various other modification will be apparent to and can be readilymade by those skilled in the art without departing from the scope andspirit of this invention. Accordingly, it is not intended that the scopeof the claims appended hereto be limited to the description as set forthherein.

What is claimed is:
 1. A monopulse radar system that detects an azimuthdepending upon amplitude difference or phase difference between signalsrespectively received by plural receiving antennas, wherein: an arrayantenna composed of plural antenna elements is used for each of atransmitting antenna and the receiving antenna; at least one of thetransmitting antenna and the receiving antenna is provided with anantenna switch for switching an antenna beam shape to a sharp angle/longdistance or a wide angle/short distance; and a switch control devicethat controls the switching of the antenna switch is provided.
 2. Amonopulse radar system according to claim 1, wherein: when the antennaswitch connects or disconnects antenna element groups forming the arrayantenna, an antenna beam shape is switched to a sharp angle/longdistance or a wide angle/short distance.
 3. A monopulse radar systemaccording to claim 1, wherein: the transmitting and receiving antenna isformed by a transmitting and receiving common antenna composed of pluralantenna elements.
 4. A monopulse radar system according to claim 1,comprising: a switch control device that controls the switching of theantenna switch every fixed time.
 5. A monopulse radar system accordingto claim 1, comprising: a switch control device that controls theswitching of the antenna switch according to distance between a mobilebody and an obstacle.
 6. A monopulse radar system used for a car thatdetects an azimuth depending upon amplitude difference or phasedifference between signals respectively received by plural receivingantennas, wherein: an array antenna composed of plural antenna elementsis used for each transmitting antenna and each receiving antenna; atleast one of the transmitting antenna and the receiving antenna isprovided with an antenna switch for switching an antenna beam shape to asharp angle/long distance or a wide angle/short distance; and a switchcontrol device that controls the switching of the antenna switchaccording to position information from a position information retrievalsystem mounted on a mobile body is provided.
 7. A monopulse radar systemaccording to claim 6, wherein: when the antenna switch connects ordisconnects antenna element groups forming an array antenna, an antennabeam shape is switched to a short angle/long distance or a wideangle/short distance.
 8. A monopulse radar system according to claim 6,comprising: a switch control device that controls the switching of theantenna switch according to distance between a mobile body and anobstacle.